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Introduction to

Nondestructive Testing

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Methods of NDT

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What are Some Uses

of NDE Methods?

Flaw Detection and Evaluation

Leak Detection

Location Determination

Dimensional Measurements

Structure and Microstructure Characterization

Material Sorting and Chemical Composition

Determination

Fluorescent penetrant indication

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Common NDT Methods

Visual Liquid Penetrant Magnetic Ultrasonic

X-rayEddy Current

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VISUAL TESTING

To support other NDT methods

Direct unaided and aided

Stages of Inspection

Tools

Merits Demerits

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Most

basic and common

inspection method.

Tools include fiber

scopes, borescopes,

magnifying glasses and

mirrors.

Robotic crawlers permit

observation in hazardous or

tight areas, such as air

ducts, reactors, pipelines.

Portable video inspection

unit with zoom allows

inspection of large tanks

and vessels, railroad

tank cars, sewer lines.

Visual Inspection

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Throat measurement

using a Palmgren

gage.

Leg size

determination with

fillet gage.

Convexity measurement

with VWAC gage.

Measurement of undercut depth

with VWAC gage.

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Basic Process of PT

1) Clean Dry Component

4) Apply Developer

2) Apply Penetrant

3) Remove Excess

5) Visual Inspection

6) Post Clean Component

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Basic Process of PT

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Choices of Penetrant Materials

Penetrant Type

I Fluorescent

II Visible

Method

A Water Washable

B Postemulsifiable - Lipophilic

C Solvent Removable

D Postemulsifiable - Hydrophilic

Developer Form

Dry Powder

Wet, Water Soluble

Wet, Water Suspendable

Wet, Non-Aqueous

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A liquid with high surface wetting characteristicsis applied to the surface of the part and allowed

time to seep into surface breaking defects.

The excess liquid is removed from the surfaceof the part.

A developer (powder) is applied to pull thetrapped penetrant out the defect and spread it

on the surface where it can be seen.

Visual inspection is the final step in the

process. The penetrant used is often loaded

with a fluorescent dye and the inspection is

done under UV light to increase test sensitivity.

Liquid Penetrant Inspection

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Magnetic Particle Inspection

The part is magnetized. Finely milled iron particles coatedwith a dye pigment are then applied to the specimen. These

particles are attracted to magnetic flux leakage fields andwill cluster to form an indication directly over thediscontinuity. This indication can be visually detected underproper lighting conditions.

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Magnetic Particle TestingThe flaw (for example, a crack) is located

from the "flux leakage", following theapplication of fine iron particles, to the

area under examination. There are

variations in the way the magnetic field

is applied.

N S

IRON POWDER

S NN S

IRON POWDER

CRACK

CRACK

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Film Radiography

Top view of developed film

X-rayfilm

The part is placed between the radiationsource and a piece of film. The part will stop

some of the radiation. Thicker and more

dense area will stop more of the radiation.

= more exposure

= less exposure

The film darkness (density) willvary with the amount of radiation

reaching the film through the test

object.

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Radiographic Images

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High frequency sound waves are introduced into a material andthey are reflected back from surfaces or flaws.

Reflected sound energy is displayed versus time, and inspector canvisualize a cross section of the specimen showing the depth offeatures that reflect sound.

f

plate

crack

0 2 4 6 8 10

initialpulse

crack

echo

back surfaceecho

Oscilloscope, or flaw

detector screen

Ultrasonic Inspection (Pulse-Echo)

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Ultrasonic Testing

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Common Application of NDT

Inspection of Raw Products Inspection Following

Secondary Processing In-Services DamageInspection

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Inspection of Raw Products

Forgings,

Castings, Extrusions, etc.

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Machining Welding Grinding

Heat treating Plating etc.

Inspection Following

Secondary Processing

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CrackingCorrosion

Erosion/WearHeat Damageetc.

Inspection For

In-Service Damage

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Power Plant Inspection

Probe

Signalsproduced by

variousamounts ofcorrosionthinning.

Periodically, power plants are

shutdown for inspection.Inspectors feed eddy currentprobes into heat exchanger tubesto check for corrosion damage.

Pipe with damage

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Wire Rope Inspection

Electromagnetic devices and visualinspections are used to find broken

wires and other damage to the wirerope that is used in chairlifts, cranesand other lifting devices.

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Storage Tank Inspection

Robotic crawlers use

ultrasound to inspectthe walls of largeabove ground tanks forsigns of thinning dueto corrosion.

Cameras on longarticulating arms

are used to inspectundergroundstorage tanks fordamage.

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Aircraft Inspection

Nondestructive testing is usedextensively during the

manufacturing of aircraft. NDT is also used to find cracks andcorrosion damage duringoperation of the aircraft.

A fatigue crack that started at the

site of a lightning strike is shownbelow.

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Jet Engine Inspection

Aircraft engines are overhauledafter being in service for a period of

time. They are completely disassembled,cleaned, inspected and thenreassembled.

Fluorescent penetrant inspection is

used to check many of the parts forcracking.

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Pressure Vessel Inspection

The failure of a pressurevessel can result in the rapid

release of a large amount ofenergy. To protect againstthis dangerous event, thetanks are inspected usingradiography and ultrasonic

testing.

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Rail Inspection

Special cars are used to inspect

thousands of miles of rail to findcracks that could lead to aderailment.

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Bridge Inspection

The US has 578,000highway bridges.

Corrosion, cracking andother damage can allaffect a bridgesperformance.

The collapse of the Silver

Bridge in 1967 resultedin loss of 47 lives.

Bridges get a visualinspection about every 2years.

Some bridges are fittedwith acoustic emissionsensors that listen forsounds of cracksgrowing.

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NDT is used to inspect pipelines toprevent leaks that could damage theenvironment. Visual inspection,radiography and electromagnetictesting are some of the NDT methodsused.

Remote visual inspection usinga robotic crawler.

Radiography of weld joints.

Magnetic flux leakage inspection. Thisdevice, known as a pig, is placed in thepipeline and collects data on thecondition of the pipe as it is pushed

along by whatever is beingtransported.

Pipeline Inspection

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Special Measurements

Boeing employees in Philadelphia were given the privilege ofevaluating the Liberty Bell for damage using NDT

techniques. Eddy current methods were used to measure theelectrical conductivity of the Bell's bronze casing at variouspoints to evaluate its uniformity.

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For More Information on NDT

The Collaboration for NDT

Education

www.ndt-ed.org

The American Society

for Nondestructive

Testing

www.asnt.org

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THANK YOU

S.PONNAPPAN

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Eddy Current Testing

Eddy current testing is particularly well suited for detectingsurface cracks but can also be used to make electrical

conductivity and coating thickness measurements. Here a smallsurface probe is scanned over the part surface in an attempt todetect a crack.

LIMITATIONS OF DPT

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LIMITATIONS OF DPT

- Poor repeatability of test.

- Retest should be done with same type of

penetrant only.

- Can not give the indication for depth.

- Not suitable for porous material.

- Not applicable for hidden defects.